Simplify interval hooks since there is only one bridge threading model now.

* Convert interval timers to use the ast_waitfor_nandfds() timeout.

* Remove bridge channel action for intervals.  Now the main loop handles
running interval hooks.


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@395340 f38db490-d61c-443f-a65b-d21fe96a405b